Ablation of living tissue has been used as a therapeutic intervention to cure or improve certain disease states. More specifically, ablation of cardiac tissue has been used to treat a variety of cardiac rhythm disturbances, including those originating in both the atria (upper chambers) and ventricles (lower chambers). Most of these techniques involve the utilization of an energy source (radiofrequency energy, cryothermy, microwave, ultrasound or laser) to destroy living tissue and render such tissue into a scar that is incapable of conducting electrical energy. Regarding atrial fibrillation specifically, most ablative strategies target the pulmonary vein orifices and their transitions to the left atrium, while others are meant to create linear scar lesions within and around the left and right atria themselves. In another technique, balloon cryoablation of the pulmonary vein orifices, creates broad circular lesions by freezing the areas where a balloon is placed to occlude the pulmonary vein, ideally at its junction with the left atrium proper. All of these strategies aim to either encircle or “box-in” target areas, or focally interrupt areas considered to be important sources of atrial fibrillation (always with a major focus on the pulmonary veins).
More recently, the role of the posterior wall of the left atrium heart chamber has been recognized as significant in more “advanced” forms of atrial fibrillation, and its role in “sustaining” atrial fibrillation, possibly by becoming hyperconductive due to eccentric scar formation. It has been postulated that thorough ablation of both the pulmonary vein origins and the entire posterior wall of the left atrium would be a very effective strategy specifically for advanced forms of atrial fibrillation (including persistent cases), and methods to implement this strategy have been emerging, but the tools are somewhat limited. While pulmonary vein ablation strategies work well in patients with smaller left atrium heart chambers and those who have earlier stage atrial fibrillation (paroxysmal or intermittent), many patients have more persistent forms of atrial fibrillation that cannot be treated successfully with pulmonary vein ablation (or “isolation”) alone. There have been attempts to ablate the posterior wall of the left atrium from “within” the left atrium, but in order to be effective, many lesions need to be delivered, each with a small but finite risk of other organ injury, including the airway and the esophagus.
Older surgical strategies (cut-and-sew Maze procedure) have shown reproducible success in these advanced cases, but the surgeries can be risky (require use of the heart-lung machine and cardiac arrest). Attempts to reproduce the extensive surgical lesions using minimally invasive techniques or less invasive tools (compared with “cut and sew”) showed some promise, but success rates have been modest and the “minimally invasive” nature has still been considered by most to be substantially invasive.
Among atrial fibrillation experts, it has been widely agreed that anatomically, the pulmonary vein transitions are the source of most of the irregular voltage that typically initiates atrial fibrillation, but in advanced cases, the posterior aspect (back wall) of the left atrium somehow sustains the process of atrial fibrillation, even if the pulmonary veins have been ablated to be electrically isolated from the left atrium. Unfortunately, catheter-based strategies that aim to treat the posterior wall from the inside of the atrium are much more risky procedures than usual because of potential damage to contiguous structures, such as the esophagus, that lie right behind the left atrium that can be injured by inappropriate energy delivery. Further, the results with catheter treatment (called CFAE ablation: complex fractionated atrial electrograms) vary dramatically because the catheter treatment lesions (burns or freezes) are far too small (like point- or spot-welding) to effectively treat (ablate) large and contiguous areas of posterior left atrial tissue. More recently, a linear ablation device has been used that can ablate multiple small strips of the posterior left atrium from the outside (avoiding damage to contiguous organs like the airway and esophagus), but in a piece-meal fashion. The approach has demonstrated good proof of principle for treating persistent forms of atrial fibrillation with a limited experience. The method seems to be more effective than “within-the-left atrium” approaches (catheter ablation), but is tedious to use, as it was intended as a device that creates roughly 3 cm×0.5 cm linear lesions to mimic aspects of the cut-and-sew Maze procedure, but is an imperfect device and method to treat the entire posterior left atrium as it comprises a much larger surface. Another important limitation is that radiofrequency energy algorithms typically self-limit energy delivery with increasing impedance (resistance) of the target tissue, such as occurs with the presence of epicardial fat, which sometimes insulates the posterior left atrial surface and may significantly inhibit ablation. Further, reaching certain parts of the posterior left atrium requires a level of technical proficiency that may be difficult to reproducibly achieve. Since atrial fibrillation is a serious disease that affects one in four Americans over 40 at some point in their lifetime, a treatment that is efficacious/reproducible, less invasive, quick, and easy to learn and apply has dramatic appeal and could save the healthcare system billions of dollars.